Temperature-dependent growth rates of Alaskan ‘shallow-water’ flatfish species Tom Hurst, Michele Ottmar, Cliff Ryer Fisheries Behavioral Ecology Program Alaska Fisheries Science Center NOAA-NMFS Newport, OR Flatfishes in Alaska

• 24 Species recorded in Alaskan waters • ~ 15 species common in Gulf of Alaska and/or Bering Sea • 14 species commercially harvested • 2011 – 2015 average > 250,000 MT/y ~ $225 M/y

• Most important species Yellowfin sole – largest landings of any flatfish in world Rock sole (northern + southern) – second largest landings Pacific halibut – most valuable – over $130 M/y commercial + important recreational + subsistence fisheries

Compiled from: Mecklenburg et al. 2002. Fishes of Alaska NOAA Commercial fishery statistics website NMFS 2014. Fisheries economics of the United States Species distributions – “shallow water complex”

Northern rock sole Yellowfin sole

Pacific halibut Alaska plaice

English sole Longhead dab

All six species reside in shallow coastal nurseries as juveniles.

Adult distributions from Matarese et al. 2003 LHD distribution from Mecklenburg et al. 2002 Temperature-dependent growth rates.

Northern rock sole Temperature-dependent growth rates of juveniles measured by Ryer, Hurst, & Boersma. 2012

Pacific halibut

English sole Objectives: Measure temperature-dependent growth rates of Yellowfin sole Alaska plaice Longhead dab

Compare thermal responses among 6 Alaskan flatfishes

Contrast yellowfin sole and northern rock sole thermal sensitivity, habitat, distribution, and climate responses. Fish collections

Collection locations: YFS: Kodiak, AK AKP: Nome, AK LHD: Nome, AK

NRS: Kodiak, AK PH: Kodiak, AK ES: Newport, OR

Fish collected from nearshore waters 3-20 m depth Otter trawl & beam trawl Held for several days at collection site

Overnight shipment to AFSC laboratory on campus of OSU in Newport, OR Experimental facilities

Because of logistical constraints associated with fish numbers and quarantine requirements for some species, we had to do experiments in two different sets of tanks.

“large” round tanks, n=15 “small” rectangle tanks, n=32

Used for: NRS, PH, ES, LHD Used for: YFS, AKP, PH

Crossover: LHD measured in tanks used for earlier studies Additional PH expt in small tanks at 9°C Experimental protocols

Tank mean growth rates used in all analyses Number of independent tanks = 10-16 per species

Fish acclimated to laboratory culture for at least 2 months prior use in experiments. Extended low temperature range to 2°C for AKP, YFS, LHD. Fish acclimated to test temperatures at approx. 1.5°C / day Acclimated for 2 weeks prior to measuring growth rates. Fish fed ad libitum once per day; “gel food” Measured 3-5 times at 2 week intervals

Individual fish identified through size-rank differences except YFS & Supplemental PH experiment; RFID PIT tags in body cavity Analyses based on tank mean growth rates Growth and survival

Alaska plaice

High survival to temperatures where growth drops off. Growth and survival

Alaska plaice Yellowfin sole

High survival to temperatures Survival declined above where growth drops off. temperature of maximum growth. Growth and survival

Alaska plaice Longhead dab Yellowfin sole

High survival to temperatures Survival declined above Low survival at temperatures where growth drops off. temperature of maximum above 10°C, but surviving fish growth. had high growth. *Not size-dependent. Comparison growth rates patterns across studies

Ryer et al. 2012.

See generally similar patterns. Extended experiments to lower temperatures. Stronger effects observed at the highest temeratures. Comparison growth rates patterns across studies???

But overall slower growth observed in AKP, YFS, LHD than NRS, PH, ES

Are there methodological differences that can explain the lower rates observed in the current study. Halibut experiment comparison

An experiment on juvenile halibut conducted in 2016, at the same time as the YFS experiment allowed us to evaluate the potential for procedural differences between experiments.

Ryer et al. 2012 Hurst and Planas, unpublished* Growth at 9°C tested 5, 9, 13, 16° tested 2 and 9°C < 10% difference “large” round tanks “small” tanks in SGR 7 fish per tank 5 fish per tank not tagged internal RFID tags mean 69.5 mm TL mean 66.7 mm TL

*Talk by Planas and Hurst, Tuesday 11am. Size effects?

Not enough size variation within each experiment to describe size-dependent variation in growth. PH NRS ES 16° 13° 16° But, likely not enough to be responsible for the observed differences in measured rates.

AKP YFS 13° 13° LHD 16° Size effects? Age effects?

But, because of differences in the timing of spawning and settlement:

PH Age 0 NRS ES 16° NRS, PH, ES were collected as age-0 13° 16° AKP, YFS, and YFS were collected as age-1

Age 1 AKP YFS 13° 13° LHD Similar patterns observed among juvenile gadids. 16°

Is there an age effect on growth potential, independent of the general decline in SGR with increasing size.

H0: age-0 (pre-first winter) fish are “different” than age-1 (post-first winter)?

Laurel et al. 2016 Comparing temperature sensitivity among species

Calculate temperature of maximum SGR

Calculate temperature range to 50% SGR LHD Representative? High mortality at these temps.

Eurythermic

Delta T Stenothermic Implications for climate change

The “Blob” – extensive area of warm waters Yellowfin sole may be most sensitive to climate change over the N. Pacific & Bering Sea because of their high thermal sensitivity.

Already have field evidence of sensitivity. Interannual variation in growth reflects thermal sensitivity

Matta et al. 2010. MEPS.

Collected NRS, AKP, and YFS from Bering Sea where the species distrubutions overlap.

Look at synchrony and climate drivers of annual growth rates.

Otolith ring width index based on within individual, across year variation. Interannual variation in growth reflects thermal sensitivity

Eurythermic

Stenothermic Eurythermic

Stenothermic

What about other parts of the distribution? Northernmost range Northern rock sole General models would predict that warming would allow northern rock sole to expand farther north, occupying waters currently inhabited by YFS and AKP.

But, coastal temperatures do not follow latitudinal trends.

Yellowfin sole

X

Warming may reduce habitat suitability for the high latitude species even in the northern part of their range. Summary

Differences among species in thermal sensitivity. YFS have high thermal sensitivity and live in the most thermally variable environments. Growth responses did not match survival patterns in LHD.

YFS will be more sensitive to climate changes. Climate change may alter habitat use throughout their range.

Future: 1. Repeat experiments across ages to clarify size and age effects. 2. Perform temperature preference experiments – link performance to preference. 3. Spatially explicit model of seasonal growth potential.

Broader: Explore how to integrate field and laboratory studies to improve understanding of climate and habitat interactions on fish distributions and productivity.